The SC213 and SC216 chassis are 2 rack-units in size and both include single edge-expander versions. The SC216 series also has a model, the SC216E2-R900, which has dual edge expanders for data path failover protection. The SC216-E1-R900 is a single edge expander that can cascade up to 240 physical devices. Another model, the CS213E!-R900 can also cascade up to 240 physical devices.